1. Field of the Invention
The present invention relates to a method of removing silicon dioxide from a solution or equipment. More particularly, the present invention relates to a method of removing SiO2 from a waste liquid, to a method of cleaning a membrane tube for processing waste water containing SiO2, and to a method of processing waste water containing SiO2.
2. Description of the Related Art
In the semiconductor industry, waste water from chemical mechanical polishing (CMP) processes is always a big problem to all semiconductor fabs over the world. The composition of CMP waste water is quite complicated and includes a large amount of solid suspension. Methods of processing CMP waste water are generally divided into two categories, wherein the first one utilizes chemical coagulation to treat CMP waste water without recovery, and the second one utilizes filtration for recovery.
Because the amounts of SiO2 particles and other solid particles are quite large in CMP waste wafer, the membrane tube used for filtration is easily clogged and therefore has a short lifetime. When a membrane tube is seriously clogged with SiO2, a highly basic solution is conventionally used to remove the clog in consideration that SiO2 has higher solubility in a high-pH environment. However, since SiO2 is dissolved merely in a concentration of about 1000 ppm in an environment of pH>12 and requires ling-time dip and stir for dissolution, the effect of the method is too insufficient to solve the clogging issue of membrane tubes.
Moreover, the method of removing clog with a highly basic solution is merely based on a physical mechanism without any chemical reaction, so that the cleaning efficiency is quite low. Since the cleaning effect is insufficient, a membrane tube has to be replaced after being used for 30 months due to serious clogging, so that much manpower and money are consumed.